Method for coating metal surfaces of substrates and objects coated in accordance with said method

ABSTRACT

The invention relates to a method for coating surfaces, to a corresponding coating, and to the use of the objects coated in accordance with said method. The invention relates to a method for coating metal surfaces of substrates, comprising or consisting of the following steps: I. providing a substrate having a cleaned metal surface, II. contacting and coating metal surfaces with an aqueous composition in the form of a dispersion and/or suspension, IX. optionally rinsing the organic coating, and X. drying and/or baking the organic coating or XI. optionally drying the organic coating and coating with a coating composition of the same type or a further coating composition before a drying process and/or baking process, wherein in step II the coating is performed with an aqueous composition in the form of a dispersion and/or suspension containing 2.5 to 45 wt % of at least one non-ionic stabilized binder and 0.1 to 2.0 wt % of a gelling agent, wherein the aqueous composition has a pH value in the range of 0.5 to 7 and forms, with the cations eluted from the metal surface in the pretreatment step and/or during the contacting in step II, a coating based on an ionogenic gel.

REFERENCE TO RELATED APPLICATIONS

This is a National Stage entry of International Patent ApplicationPCT/EP2014/064857, filed on Jul. 10, 2014, which application claimspriority from German Application No. 102013213498.3, filed Jul. 10,2013. Each patent application identified above is incorporated herein byreference in its entirety.

The invention relates to a method for coating surfaces, a correspondingcoating and the use of the objects coated according to this method.There are numerous methods for producing homogeneous coatings onmetallic surfaces in particular by means of immersion methods. In doingso, the following techniques are preferably used for creatinganticorrosion coatings consisting primarily of an organic matrix and/ororganic and/or inorganic additive components.

The traditional methods are based on use of the rheological propertiesof the formulations that are used in order to achieve a complete coatingof a joined workpiece. Although an accumulation of coating material incritical locations can be reduced by continuous rotation of therespective workpiece after the immersion process, it is impossible withthis method to achieve a completely homogeneous coating. In addition,defects such as bubbles and pits that have a negative effect on thequality of the coating as a whole may occur in locations with largeramounts of coating during the drying and/or crosslinking process.

Electrophoretic methods avoid these problems by using an electriccurrent to deposit a uniform coating in immersion. With this method itis possible to homogeneous coatings on metallic workpieces. The coatingsthat are deposited exhibit extremely good adhesion in the wet state tothe metallic substrate, which allows treatment of the workpiece in asubsequent rinsing step without separation of the coating. As a result,the aforementioned locations on the workpiece which are difficult toaccess can be freed of excess coating solution and therefore no defectscan be formed during the drying process. This technique has thedisadvantage that, in addition to the amount of electricity requiredand, in addition to suitable immersion basins, which result in increasedcosts and also so-called edge alignment, occur because electric fieldsare built up non-homogeneously on macroscopic edges, and the edges arecoated uniformly and possibly even incompletely. In the design of theworkpieces, it is also necessary to avoid cavities because an effectcomparable to the Faraday cage phenomenon occurs in these locations.Because of the reduction in the electric field strengths required fordeposition, only a greatly reduced coating can be applied by this method(wrap-around problem) or none at all in such regions of the workpiece,which results in a negative effect on the coating quality. In addition,this technique has the following disadvantages in electro dip coating(EDC) such as in cathodic dip coating (CDC): a corresponding immersionbath has a very complex structure, including all the electric andmechanical devices of temperature management, power supply andelectrical installation, circulation devices and additional devices,including disposal of the anolyte acid formed in electrolytic coatingand with ultrafiltration for recycling the coating as well as controldevices. The process management also requires a very high technicalcomplexity, due to the high amperages and large quantities of energy inboth the standardization of the electric parameters based on the bathvolume and the accurate adjustment of all process parameters and inmaintenance and cleaning of the installation.

The known autophoretic processes are based on a currentless concept,consisting of a pickling attack on the substrate surface, in which metalions are dissolved out of the surface and an emulsion is coagulatedbecause of the concentration of metallic ions at the resultinginterface. Although these methods do not exhibit the aforementionedrestriction of the electrolytic methods with respect to the Faraday cageeffect, the coatings formed in the process must be set in a complexmultistage immersion process after the initial activation step. Inaddition, the pickling attack leads to unavoidable contamination of theactive zone by metal ions that must be removed from the zones.Furthermore, the method is based on a chemical deposition process thatis not self-regulating and cannot be terminated on demand, e.g., due topowering down the electric current in the electrolytic processes. Thus,the development of a layer that is too thick is unavoidable with alonger dwell time of the metallic substrates in the active zones.

There has long been a desire to form homogenous coatings in an immersionprocess efficiently and inexpensively in order to produce the mostclosed possible and essentially level coatings with a greater thicknessfrom them.

The object is therefore a method for coating metallic surfaces ofsubstrates, comprising or consisting of the steps:

-   I. Supplying a substrate having a cleaned metallic surface,-   II. Contacting and coating metallic surfaces with an aqueous    composition in the form of a dispersion and/or suspension,-   III. Optionally rinsing the organic coating and-   IV. Drying and/or baking the organic coating or-   V. Optionally drying the organic coating and forming another coating    having a similar or additional coating composition before drying    and/or baking,    wherein in step II, the coating is applied with an aqueous    composition in the form of a dispersion and/or suspension containing    2.5 to 45 wt % of at least one nonionically stabilized binder and    0.1 to 2.0 wt % of a gelling agent, wherein the aqueous composition    has a pH in the range of 0.5 to 7 and a coating based on an    ionogenic gel is formed, with cations dissolved out of the metallic    surface in the pretreatment step and/or during the contacting in    step II.

The nonionically stabilized binder used according to the invention isselected on the basis of the test described as shown below:

-   -   1) preparing an aqueous mixture of deionized water, 0.5 wt % of        the gelling agent and 10 wt % of the dispersion to be        investigated;    -   2) adjusting the mixture to a pH of 2 to 3 with the help of        hexafluorozirconic acid;    -   3) immersing a cleaned substrate in the solution described above        for 5 minutes at room temperature;    -   4) in the case of deposition of a coating, a cross-check is        carried out (without the gelling agent); to do so, a mixture is        prepared from deionized water, 10 wt %, and the dispersion to be        investigated;    -   5) the mixture prepared in step 4) is again adjusted to a        starting pH of 2-3 by means of hexafluorozirconic acid, and    -   6) the test described in step 3) is repeated.

If an organic deposition is formed on the substrate according to step 3)and no deposition occurs in step 6) (without the gelling agent), thenthe nonionically stabilized binder is suitable for the method accordingto the invention.

The coating according to the invention has a single layer structure,wherein either a more or less homogenous coating is formed or a coatingin which the (polymer) particles accumulate to a somewhat greater extentclose to the metallic surface is formed and/or may occur.

According to the invention, the substrates with a metallic surface to becoated are understood as follows: metals, metal-coated surfaces or metalsurfaces pretreated with primers, from which metal cations can still bereleased. In particular the term “surface(s) to be coated” in the senseof this patent application includes surfaces of metallic objects and/ormetallic particles, which may optionally be precoated with a metalliccoating based on zinc or a zinc alloy and/or with at least one coatingof a pretreatment composition or treatment composition, for example,based on chromate, Cr³⁺, Ti compound, Zr compound,silane/silanol/siloxane/polysiloxane and/or organic polymer.

Of the metallic materials, fundamentally all types of metallic materialsare possible, in particular those made of aluminum, iron, copper,titanium, zinc, tin and/or alloys containing aluminum, iron, steel,copper, magnesium, nickel, titanium, zinc and/or tin, wherein they mayalso be used side by side and/or one after the other. The materialsurfaces may optionally also be precoated, for example, with zinc or analloy containing aluminum and/or zinc.

Fundamentally all types of objects made of a metallic material orprovided with at least one metallic coating may be used as the object tobe coated. Especially preferred objects include in particular strips(coils), sheet metal, parts such as small parts, joined components,components with complex shapes, profiles, rods and/or wires.

The term “currentless coating” in the sense of this patent applicationmeans that in contrast with the known electrolytic methods for producingthe follow-up coating, an electric voltage of less than 100 V is appliedexternally in coating with the composition containing the solutionand/or dispersion (=suspension and/or emulsion) in contrast with theknown electrolytic methods for producing the follow-up coating.

The invention preferably relates to a method in which the gelling agenta) contains or consists of at least one polysaccharide, based onglycogens, amyloses, amylopectins, calloses, agar, algins, alginates,pectins, carrageenan, celluloses, chitins, chitosans, curdlans,dextrans, fructans, collagens, gellan gum, gum arabic, starch, xanthans,gum tragacanth, karayans, tara gum and glucomannans; b) at least onegelling agent of natural origin, based on polyamino acids, collagens,polypeptides, lignins and/or c) at least one synthetic gelling agent,based on polyamino acids, polyacrylic acids, polyacrylic acidcopolymers, acrylamide copolymers, lignins, polyvinyl sulfonic acid,polycarboxylic acids, polyphosphoric acids or polystyrenes.

The gelling agent especially preferably contains or consists of at leastone polysaccharide based on pectins and/or gellan gum.

The method according to the invention is preferably one in which theaqueous composition and/or the organic coating produced from it containsat least one type of cations selected from those based on salts with acationic effect, selected from the group consisting of melamine salts,nitroso salts, oxonium salts, ammonium salts, salts with quaternarynitrogen cations, salts of ammonium derivatives and metal salts of Al,B, Ba, Ca, Cr, Co, Cu, Fe, Hf, In, K, Li, Mg, Mn, Mo, Na, Nb, Ni, Pb,Sn, Ta, Ti, V, W, Zn and/or Zr.

The term “copolymers” in the sense of this patent application describespolymers made up of two or more different types of monomer units.Copolymers here can be divided into five classes, as will be illustratedon the basis of a binary copolymer made up of two different comonomers Aand B:

1. Random copolymers in which the distribution of the two monomers inthe chain is random (AABABBBABAABBBABBABAB . . . );

2. Gradient copolymers, resembling random copolymers in principle, buthaving a variable amount of monomer in the course of the chain(AAAAAABAABBAABABBBAABBBBBB);

3. Alternating copolymers with a regular arrangement of the monomersalong the chain (ABABABABABABABABABAB . . . );

4. Block copolymers consisting of longer sequences or blocks of eachmonomer (AAAAAAAAABBBBBBBBBBBB . . . ), wherein depending on the numberof blocks, we can also speak of diblock, triblock, multi-blockcopolymers;

5. Graft copolymers, in which blocks of a monomer are grafted onto thebackbone of another monomer.

The term “derivatives” in the sense of this patent application denotes aderived substance having a structure similar to that of a correspondingbasic substance. Derivatives are substances, whose molecules haveanother atom or a different atomic group instead of an H atom or afunctional group and/or in which one or more atoms/atomic groups havebeen removed.

The term “polymer(s)” in the sense of this patent application denotesmonomer(s), oligomer(s), polymer(s), copolymer(s), block copolymer(s),graft copolymer(s), mixtures thereof and their compounds on an organicand/or essentially organic basis. The “polymer(s)” in the sense of thispatent application is (are) usually present primarily or entirely aspolymer(s) and/or copolymer(s).

The method according to the invention is especially preferably one inwhich the aqueous composition and/or the organic coating produced fromit contain(s) an amount of film-forming binders based on polyacrylates,polyurethanes, polyepoxides and/or their hybrids.

So-called polyacrylate-polyurethane hybrid resins of this type can bedifferentiated according to hybrid systems which are created by simplymixing the different dispersions (blends or formulations) into thosehaving a chemical bond between the different types of polymers and thosein which the different classes of polymers form interpenetratingnetworks (IPN).

Such polyurethane-polyacrylate hybrid dispersions are usually preparedby emulsion polymerization of a vinyl polymer (“polyacrylate”) in anaqueous polyurethane dispersion. However, it is also possible to producethe polyurethane-polyacrylate hybrid dispersion as a secondarydispersion.

Aqueous polyacrylate-polyepoxy hybrid dispersions are usually preparedby addition reactions of a bifunctional epoxy with bifunctional aminemonomer building blocks and then a reaction with a polyacrylate havingenough carboxyl functions. As with polyurethane secondary dispersions,water dispersibility can be achieved by carboxylate groups, for example,which have been converted into anionic groups with amines and thendispersing in water.

Hybrid dispersions for forming a layer on the substrate may preferablyalso contain, in addition to polyurethane and polyepoxy ingredients,organic polymers and/or copolymers based on polyvinyl alcohols,polyvinyl acetates, polybutyl acrylates and/or other acrylic acidesters. Acrylic acid esters are esters derived from acrylic acid(CH₂═CH—COOH) and thus having the functional group (CH₂═CH—COOR).Acrylic acid methyl esters, acrylic acid ethyl esters, acrylic acidbutyl esters and ethyl hexyl acrylate are produced in large quantities.The main use of acrylic acid esters is in homo- and copolymers whichcontain, for example, acrylic acid, acrylamides, methacrylates,acrylonitrile, fumaric acids, itaconic acid, maleates, vinyl acetate,vinyl chloride, styrene, butadiene and unsaturated polyesters,polyepoxide esters, polyacrylamides, polyacrylic acids, polycarbonates,polyesters, polyethers, polystyrene butadienes, poly(meth)acrylic acidesters, polyvinyl acetate copolymers with acrylic acid esters and/orcopolymers with dibutyl maleate and/or with vinyl esters of at least oneKoch acid, polyethylenes, polyvinyl chlorides, polyacrylonitriles,polyepoxies, polyurethanes, polyacrylates, polymethacrylates,polyesters, polyamides, polytetrafluoroethylenes, polyisobutadienes,polyisoprenes, silicones, silicone rubbers and/or their derivatives.These are present in particular in amounts of at least 50 wt % of thesolid ingredients and active ingredients in the aqueous composition.

The term “pretreatment” refers to a treatment (=bringing the surfaces tobe coated in contact with a composition, usually liquid), in whichanother coating is applied to protect the layer sequence and the objectsuch as at least one lacquer, for example, optionally after a subsequentcoating.

In the case of a prior pretreatment before activation of a surface withan activating agent that should help to electrostatically charge thesurface, the surfaces to be treated may first be given an alkalinecleaning, if necessary, and optionally brought in contact with acomposition for pretreatment, the latter in particular to form aconversion layer. Then the surfaces treated and/or coated in this waymay optionally be coated and/or optionally oiled with a primer and/orwith an optionally reshapeable protective layer, in particular with ananticorrosion primer. Oiling serves in particular to provide temporaryprotection for the treated and/or coated surfaces, in particularmetallic surfaces.

As a pretreatment, fundamentally any type of pretreatment is possible.For example, aqueous pretreatment compositions based on phosphate,phosphonate, silane/silanol/siloxane/polysiloxane, lanthanide compound,titanium compound, hafnium compound, zirconium compound acid, metal saltand/or organic polymer may be used.

In further treatment of these coated substrates, an alkaline cleaning inparticular may be performed, if needed, regardless of whether or not oilhas been applied previously.

A coating with an anticorrosion primer such as, for example, a weldingprimer can provide additional corrosion protection in particular incavities and in difficult to access sections of a substrate, whilefacilitating shapeability and/or joinability, for example, in folding,gluing and/or welding. In industrial practice, an anticorrosion primercould be used in particular when the substrate, such as sheet metal,coated with it is to be shaped after coating with the anticorrosionprimer and/or is to be joined to another component and if additionalcoatings are only then to be applied. If an anticorrosion primer isadditionally applied beneath the activation layer and beneath thepolymer coating in this set of operations, then improved corrosionprevention is usually achieved.

The term “essentially rinse-fast” in the sense of this patentapplication means that under the conditions of the respectiveinstallation and process sequence, the last coating, respectively, isnot removed entirely by a rinsing operation (=rinsing), so that acoating, preferably a closed coating, can be produced.

In the method according to the invention, a wide variety of types ofparticles, particle sizes and particle shapes may be used as theparticles.

The particles to be used in the aqueous composition for forming thelayer may preferably be oxides, hydroxides, carbonates, phosphates,phosphosilicates, silicates, sulfates, organic polymers includingcopolymers and their derivatives, waxes and/or compounded particles, inparticular those based anticorrosion pigments, organic polymers, waxesand/or compounded particles and/or mixtures thereof. They preferablyhave particle sizes in the range of 5 nm to 15 μm, from 8 nm to 5 μm orfrom 15 nm to 1.5 μm, in particular from 30 nm to 700 nm or from 50 nmto 500 nm. They are preferably water-insoluble particles.

Compounded particles have a mixture of at least two different substancesin one particle. Compounded particles may often have other substanceswith very different properties. They may, for example, contain thecomposition for a lacquer entirely or partially, optionally evencontaining substances not in particulate form, such as surfactants,defoaming agents, dispersants, lacquer aids, additional types ofadditives, dyes, corrosion inhibitors, weakly water-solubleanticorrosion pigments and/or other substances that are customary and/orknown for the corresponding mixtures. Such lacquer ingredients may besuitable and/or may often be used for organic coatings for shaping, foranticorrosion primers and other primers, for colored lacquers, fillersand/or clear lacquers.

An anticorrosion primer usually contains electrically conductiveparticles and can be welded electrically. In generally it is oftenpreferably here that a) a mixture of chemically and/or physicallydifferent particles, b) particles, aggregates and/or agglomerates ofchemically and/or physically different particles and/or c) compoundedparticles are used in the composition and/or in the particle layerformed from the composition.

In many cases, it is preferable for the composition containing theparticles and/or the particle layer formed from it to also contain inaddition to at least one type of particles, at least one non-particulatesubstance, in particular additives, dyes, corrosion inhibitors and/orweakly water-soluble anticorrosion pigments. In particular coloredparticles and/or optionally a limited amount of electrically conductiveparticles, in particular based on fullerenes and other carbon compoundswith graphite-like structures and/or carbon black, optionally also nanocontainers and/or nanotubes may also be present as particles in thecomposition and/or in the particle layer formed from it. On the otherhand, coated particles, chemically and/or physically modified particles,core-shell particles, compounded particles from various substances,encapsulated particles and/or nano containers may be used in particularas particles in the composition and/or in the coating formed from it.

With the method according to the invention, it is preferable for thecomposition containing the particles, the particle layer formed from itand/or the coating formed from it by creating a film and/or crosslinkingthe composition to contain, in addition to at least one type ofparticles, also at least one dye, one colored pigment, one anticorrosionpigment, one corrosion inhibitor, one conductivity pigment, another typeof particles, asilane/silanol/siloxane/polysiloxane/silazane/polysilazane, a lacqueradditive and/or an additive such as, for example, at least onesurfactant, one defoaming agent and/or one dispersant.

With the method according to the invention, it is preferable for thecomposition and/or the coating formed from it to contain, eitherpartially or completely, in addition to at least one type of particlesand optionally in addition to at least one non-particulate substance, achemical composition for a primer, a lacquer such as, for example, afiller, a top coat and/or a clear coat.

In many embodiments, pigments and/or additives, such as those often usedin lacquers and/or primers, are recommended as additives to the organicpolymers of the particles.

Formation of a film can be improved by use of thermoplastic polymersand/or by adding substances that serve as temporarily plasticizers.Film-forming aids act as specific solvents, which soften the surface ofthe polymer particles and thus enable their fusion. It is advantageoushere if these plasticizers remain in the aqueous composition for asufficiently long period of time, on the one hand, to be able to act onthe polymer particles for a long time and then evaporate and thus escapefrom the film. Furthermore it is advantageous if a residual watercontent is also present for a sufficiently long period of time duringthe drying process.

So-called long alcohols, in particular those having 4 to 20 carbonatoms, are advantageous as film-forming aids:

such as butanediol,

butyl glycol,

butyl diglycol,

ethylene glycol ether, such as ethylene glycol monobutyl ether,

ethylene glycol monoethyl ether,

ethylene glycol monomethyl ether,

ethyl glycol propyl ether,

ethylene glycol hexyl ether,

diethylene glycol methyl ether,

diethylene glycol ethyl ether,

diethylene glycol butyl ether,

diethylene glycol hexyl ether or a

polypropylene glycol ether such as

propylene glycol monomethyl ether,

dipropylene glycol monomethyl ether,

tripropylene glycol monomethyl ether,

propylene glycol monobutyl ether,

dipropylene glycol monobutyl ether,

tripropylene glycol monobutyl ether,

propylene glycol monopropyl ether,

dipropylene glycol monopropyl ether,

tripropylene glycol monopropyl ether,

propylene glycol phenyl ether,

trimethyl pentane diol diisobutyrate,

a polytetrahydrofuran,

a polyether polyol and/or a polyester polyol.

Crosslinking may take place, for example, with certain reactive groups,such as isocyanate groups, isocyanurate groups, phenol groups and/ormelamine groups.

The subsequent coating is preferably dried in such a manner that, inparticular, any organic polymer particles that are present can form afilm so that a larger or completely homogenous coating is formed. Inmany embodiments, the drying temperatures can be selected to be so highthat the organic polymer ingredients are able to crosslink.

In the method according to the invention, it is preferable in someembodiments that a particle layer containing essentially organicparticles is formed and is crosslinked and/or a film is formed indrying, for example. The formation of a film in many embodiments takesplace even without the presence of film-forming aids. The particles ofthe coating here preferably form a closed coating or an essentiallyclosed coating in particular when the particles are present primarily orentirely as organic polymers, in particular in drying. It is oftenpreferable for the drying temperature of a coating consisting primarilyor entirely of organic polymers to be selected, so that a closed oressentially closed coating is formed. If necessary, at least onefilm-forming may be added to form the film, in particular a film-formingaid, based on at least one long-chain alcohol. In embodiments having aplurality of particle layers one above the other, all the particlelayers are preferably applied first and then crosslinked and/or the filmis formed from them together.

The amount of at least one film-forming aid in the aqueouscomposition—in particular in the bath—may preferably be 0.01 to 50 g/L,based on the solids including the active ingredients, especiallypreferably 0.08 to 35 g/L, most especially preferably 0.2 to 25 g/L or0.5 to 16 g/L, in particular 1 to 12 g/L or 4 to 6 g/L. The weight ratioof the amounts of organic film-forming agent to the amounts offilm-forming aids in the aqueous composition—in particular in thebath—may vary in a wide range and in particular may be ≤(100:0.1). Thisratio is preferably in the range of 100:10 to 100:0.2 or from 100:2.5 to100:0.6, especially preferably in the range of 100:2 to 100:0.75 or from100:1.4 to 100:1.

It is often preferable here for the drying, film forming and/orcrosslinking to take place in the temperature range of 50 to 260° C.,especially preferably in the temperature range from 120 to 220° C.,based on the oven temperature and/or based on the peak metal temperature(PMT). The selected temperature range depends largely on the type andamount of organic ingredients and optionally also the inorganicingredients and optionally also their film-forming temperatures and/orcrosslinking temperatures.

The invention preferably relates to a method in which the aqueouscomposition and/or the organic coating produced from it contains anamount of at least one complexing agent for metal cations or a polymerwhich is modified for complexing metal cations.

The method according to the invention is preferably one in which theaqueous composition and/or the organic coating produced from it containsat least one complexing agent selected from those based on maleic acid,alendronic acid, itaconic acid, citraconic acid or mesaconic acid or theanhydrides or hemiesters of these carboxylic acids.

The aqueous composition and/or the organic coating produced from itadvantageously contain(s) at least one emulsifier.

It is especially preferable that the aqueous composition and/or theorganic coating produced from it contains at least one emulsifierselected from those based on anionic emulsifiers.

The aqueous composition and/or the organic coating produced from itpreferably contain(s) a mixture of at least two different anionicpolyelectrolytes.

The aqueous composition and/or the organic coating produced from itespecially preferably contain(s) a mixture of two pectins.

The aqueous composition and/or the organic coating produced from it alsopreferably contains as the gelling agent at least one anionicpolysaccharide selected from those with a degree of esterificationand/or a degree of amidation of the carboxy function in the range of 1to 75% based on the total number of alcohols and carboxy groups.

The aqueous composition and/or the organic coating produced from it mostespecially preferably contains as the gelling agent at least one anionicpolysaccharide and/or at least one anionic polyelectrolyte selected fromthose having a molecular weight in the range of 500 to 1,000,000g/mol⁻¹.

In the method according to the invention, it is especially preferablethat the anionic polyelectrolytes are or have been modified withadhesion-promoting adhesive groups selected from the group consisting ofchemical groups of multifunctional epoxies, isocyanates, primary amines,secondary amines, tertiary amines, quaternary amines, amides, imides,imidazoles, formamides, Michael reaction products, carbodiimides,carbenes, cyclic carbenes, cyclocarbonates, multifunctional carboxylicacids, amino acids, nucleic acids, methacrylamides, polyacrylic acids,polyacrylic acid derivatives, polyvinyl alcohols, polyphenols, polyolshaving at least one alkyl and/or aryl radical, caprolactam, phosphoricacids, phosphoric acid esters, epoxy esters, sulfonic acids, sulfonicacid esters, vinyl sulfonic acids, vinyl phosphonic acids, catechol,silanes as well as the silanols and/or siloxanes produced from them,triazines, thiazoles, thiazines, dithiazines, acetals, hemiacetals,quinones, saturated fatty acids, unsaturated fatty acids, alkyds,esters, polyesters, ethers, glycols, cyclic ethers, crown ethers,anhydrides as well as acetylacetones and β-diketo groups, carbonylgroups and hydroxyl groups.

Al, Cu, Fe, Mg and/or Zn is/are advantageously selected as the cationsthat are/have been dissolved out of the metallic surface and/or thatare/have been added to the aqueous composition.

The aqueous composition preferably also contains a crosslinking agentselected from the group consisting of silanes, siloxanes, phenolic resintypes or amines in an amount of 0.01 g/L to 50 g/L.

The aqueous composition especially preferably contains a crosslinkingagent selected from the group consisting of silanes, siloxanes, phenolicresin types or amines in an amount of 0.01 g/L to 50 g/L.

In another embodiment of the invention, the aqueous composition containscomplex titanium and/or zirconium fluorides in an amount of 0.001 g/L to500 g/L.

The aqueous composition especially preferably contains complex titaniumand/or zirconium fluorides in an amount of 0.01 g/L to 75 g/L.

The aqueous composition and/or the organic coating produced from it mostespecially preferably also contain(s) at least one additive selectedfrom additives consisting of the group of foam suppressants, biocides,dispersion aids, film-forming aids, acidic and/or basic additives foradjusting the pH and thickeners and flow control agents.

Before bringing the metallic surfaces in contact with an aqueouscomposition and coating the metallic surfaces with the aqueouscomposition in process step II, the metallic surfaces are mostespecially preferably cleaned, pickled and/or pretreated.

The aqueous composition advantageously forms a coating based onionogenic gel in which the dry film which is formed then or later has athickness of at least 1 μm.

The organic coating especially preferably is formed in 0.05 to 20minutes in an immersion bath and has a dry film thickness in the rangeof 5 to 100 μm after drying.

The invention also relates to an aqueous composition containing 2.5 to45 wt % of at least one nonionically stabilized binder and 0.1 to 2.0 wt% of a gelling agent wherein the aqueous composition has a pH in therange of 0.5 to 7.

The aqueous composition is preferably a composition that contains in thedispersion of film-forming polymers an amount of organic particles basedon polyacrylates, polyurethanes, polyepoxides and/or their hybrids, anamount of at least one complexing agent selected from those based onmaleic acid, alendronic acid, itaconic acid, citraconic acid ormesaconic acid or anhydrides or hemiesters of these carboxylic acids andat least one anionic polyelectrolyte based on pectins or gellan gum.

It has been found that closed or essentially closed coatings having alayer thickness in the range of 1 μm to 250 μm, in particular in therange of 3 μm to 100 μm or 5 μm to 50 μm, can then be prepared from thesurfaces coated according to the invention. The individual coatings mayhave corresponding layer thicknesses before and/or after theirfilm-forming step and/or before their crosslinking.

It has been found that the surfaces coated according to the inventionfrom which closed or essentially closed coatings are subsequently formedcan be produced by much simpler and much less expensive methods than,for example, electro dip coatings, autophoretic dip coatings or powdercoatings.

Furthermore, it has been found that such coatings produced according tothe invention may be equivalent in their properties to the electro dipcoatings, autophoretic dip coatings or powder coatings of industrialpractice today if formulations prepared chemically accordingly inparticular are used.

It has surprisingly been found that the method according to theinvention, which is not or essentially not an electrolytic method, evenin the event that it is supported to a minor extent by electric voltage,and therefore it is not usually necessary for an external electricvoltage to be applied, can be operated easily without complex controls.This method can be used in a broad temperature range and even at roomtemperature, if the subsequent drying is omitted.

It has surprisingly been found that in the case of the method accordingto the invention, no complex control measures are required with respectto the application of the activating means in order to achieve a uniformand homogeneous coating and that high quality protective follow-upcoatings are formed with a low consumption of chemicals, these coatingsachieving thickness in the range of 500 nm to 30 μm.

It has surprisingly been found that the method according to theinvention is a self-regulating method with regard to the deposition ofthe follow-up coating in particular and that no complex control measuresare necessary in this method and high quality protective coatings areformed with a low consumption of chemicals.

It has surprisingly been found that the follow-up coatings depositedaccording to the invention form a homogenous layer with a uniform drylayer thickness even on a workpiece having a complex shape, and thatthese coatings are comparable in quality to a traditional paint layerapplied by traditional electrophoretic or autophoretic depositionmethods.

The coating according to the invention can preferably be used for coatedsubstrates as wire, wire mesh, strip, sheet metal, profile, lining,parts for a vehicle or a flying object, elements for a householdappliance, elements in construction, frameworks, guide rails, heatingelements or fence elements, molded parts of a complex geometry or smallparts such as screws, nuts, flanges or springs. It is especiallypreferably used in automotive engineering, construction, for appliancebuilding, for household appliances or in the heating sector. Use of themethod according to the invention is especially preferred for coatingsubstrates, which have posed problems in coating with an electro dipcoating.

The invention will now be explained in greater detail below on the basisof 16 exemplary embodiments and two comparative examples, using assubstrates in step I:

-   I. 1: Electrolytically galvanized steel plate with a zinc layer    thickness of 5 μm, sheet metal thickness 081 mm;    -   2: Cold rolled steel, sheet metal thickness approximately 0.8        mm;    -   3: Aluminum alloy of grade AC 170, sheet metal thickness        approximately 1.0 mm and the following general treatment step        are carried out;-   II. Alkaline cleaning    -   30 g/L Gardoclean® S 5176 and 4 g/L Gardobond® Additive H 7406        from Chemetall GmbH prepared in drinking water according to        DIN 2000. The sheet metal plates were cleaned for 180 s by        spraying at 60° C. and then rinsed for 120 s within drinking        water and 120 s with deionized water by immersion.-   III. 1. Pretreatment based on zinc phosphate (Gardobond 26S of the    company Chemetall GmbH)    -   2. Pretreatment based on silane (Oxsilan 9810/2 from the company        Chemetall GmbH)

All the mixtures were applied to the respective substrate within 5minutes by dipping at room temperature.

The pH values of the entire formulation were adjusted by means ofaqueous solutions of phosphoric acid (10%) and ammonia (10%).

Binders

1: Dispersion A

Nonionically stabilized dispersion with a solids content of 50-54%, a pHof 5.0-6.0, a viscosity of 1500-3000 mPas and a density of 1.079 g/cm³.The data in the table is based on the amount of solution per liter offormulation and the resulting solids content is based on theformulation.

2: Dispersion B

Nonionically stabilized dispersion with a solids content of 50-54%, a pHof 5.0-6.0, a viscosity of 300-1500 mPas and a density of 1.079 g/cm³.The data in the table is based on the amount of solution per liter offormulation and the resulting solids content is based on theformulation.

3: Dispersion C

Anionically stabilized polyacrylate dispersion with a solids content of40%, a pH of 3.0-5.0, a viscosity of 500-3000 mPas, a density of 1.04g/cm³, particle size of approximately 160 mm and an OH number ofapproximately 25 mg KOH/g (solid resin). The data in the table is basedon the amount of solution per liter of formulation and the resultingsolids content is based on formulation.

Gelling Agent

A 1:1 mixture of polysaccharide with a molecular weight of approximately70,000 g/mol, a degree of amidation of 11%, a degree of esterificationof 41%, a degree of epoxidation of 0%, a galacturonic acid content of88% and a polysaccharide with a molecular weight of approximately 70,000g/mol, a degree of amidation of 0%, a degree of esterification of 38%, adegree of epoxidation of 0%, a galacturonic acid content of 85% are usedas the gelling agent. To prepare the formulation, a 2% aqueous solutionof the polysaccharide was used. The data in the table is based on theamount of solution per liter of formulation.

Additives

-   1: Hexafluorotitanic acid as an aqueous solution (20%) was used. The    data in the table is based on the amount of solution per liter of    formulation.-   2: Hexafluorozirconic acid was used as an aqueous solution (20%).    The data in the table is based on the amount of solution per liter    of formulation.-   3: 3-(Triethoxysilyl)propylamine (AMEO) was used. The data in the    table is based on the amount of solution per liter of formulation.

Pigments

-   1: Gas black RCC pigment concentrate based on a dispersion resin for    applications in aqueous coating systems with pH values in the acidic    range, with a pigment content of 30%, a solids content of 38% and a    density of 1.17 g/cm³.-   2: Inorganically coated white pigment based on a titanium dioxide    rutile with a titanium dioxide content of 92%.-   3: Micronized white pigment based on a titanium dioxide rutile, with    organic and inorganic coatings.

Defoaming Agent

-   1: Defoaming agent based on natural oils, emulsifiers and containing    1 wt % of the as-delivered form in water. The data in the table is    based on the amount of solution per liter of formulation.

IV: Rinsing the Organic Coating:

The rinse after the organic coating serves to remove non-adheringconstituents of the formulation and agglomerates of the formulation andto make the process sequence as close to reality as possible in theautomobile industry because the rinsing with water is usually performedeither as a dip rinse or as a spray rinse in the automobile industry.

V: Drying and/or Crosslinking the Coating

Drying or drying with film formed of the organic polymer ingredient inparticular:

-   -   175° C. for 15 minutes

Parallel studies using an eddy current measurement device and scanningelectron microscopy (SEM) have illustrated the fact that coatingsaccording to the invention are produced, and then closed or mostlyclosed coatings can be formed from them by bringing the surfaces incontact with dispersions and/or formulations.

EXAMPLE 1

Substrate 1 was coated with a mixture consisting of 10 wt %, based onthe total amount of the resulting mixture of dispersion A, and 0.5 wt %of the gelling agent, based on the total amount of the resultingmixture. If necessary, the mixture was adjusted to a pH of 2 with acid,preferably nitric acid and/or phosphoric acid, before being used. A dryfilm thickness of 20-30 μm was determined, based on measurements with aneddy current measurement instrument and SEM.

EXAMPLE 2

Experiment 1 was repeated with substrate 2 and a dry film thickness of10-20 μm was determined by SEM.

EXAMPLE 3

Substrate 1 was coated with a mixture consisting of 10 wt %, based onthe total amount of the resulting mixture of dispersion A and 0.5 wt %of the gelling agent, based on the total amount of the resultingmixture. The mixture was adjusted to a pH of 4 before use with acid,preferably nitric acid and/or phosphoric acid. Substrate 1 waspretreated according to III.1 by phosphating. A dry film thickness of7-10 μm was determined based on a measurement with an eddy currentmeasurement device and SEM.

EXAMPLE 4

Experiment 3 was repeated with substrate 2 and a dry film thickness of7-10 μm was also determined with SEM.

EXAMPLE 5

Substrate 1 was coated with a mixture consisting of 10 wt %, based onthe total amount of the resulting mixture, of dispersion A, and 0.5 wt %of the gelling agent, based on the total amount of the resultingmixture. If necessary, the mixture was adjusted to a pH of 4 with acid,preferably nitric acid and/or phosphoric acid, before use. Substrate 1was pretreated with a silane according to III.2. A dry film thickness of7-10 μm was determined, based on measurements with an eddy currentmeasurement device and SEM.

EXAMPLE 6

Experiment 5 was repeated with substrate 2, and a dry film thickness of7-10 μm was also determined using SEM.

EXAMPLE 7

Substrate 1 was coated with a mixture consisting of 5 wt % based on thetotal amount of the resulting mixture, of dispersion A and 0.5 wt % ofthe gelling agent, based on the total amount of the resulting mixture.Before use, the mixture was adjusted to a pH of 2 with acid, ifnecessary, preferably nitric acid and/or phosphoric acid. A dry filmthickness of 10-15 μm was determined, based on measurement with an eddycurrent measurement device and SEM.

EXAMPLE 8

Experiment 7 was repeated with substrate 2, and a dry film thickness of8-12 μm was also determined with SEM.

EXAMPLE 9

Substrate 1 was coated with a mixture consisting of 10 wt %, based onthe total amount of the resulting mixture, of dispersion B and 0.5 wt %of the gelling agent, based on the total amount of the resultingmixture. Before use, the mixture was adjusted to a pH of 4 with acid,preferably nitric acid and/or phosphoric acid, if necessary. A dry filmthickness of 5-8 μm was determined, based on measurements with an eddycurrent measurement device and SEM.

EXAMPLE 10

Experiment 9 was repeated with substrate 2 and a dry film thickness of8-12 μm was also determined with SEM.

EXAMPLE 11

Substrate 1 was coated with a mixture consisting of 10 wt %, based onthe total amount of the resulting mixture, of dispersion A and 0.5 wt %of the gelling agent, based on the total amount of the resultingmixture. Before use, the mixture was adjusted to a pH of 2 with acid,preferably nitric acid and/or phosphoric acid, if necessary. As anadditive, 0.4 g/L hexafluorotitanic acid was added. A dry film thicknessof 35-40 μm was determined, based on measurement with an eddy currentmeasurement device and SEM.

EXAMPLE 12

Experiment 11 was repeated with substrate 2, and a dry film thickness of20-25 μm was also determined with SEM.

EXAMPLE 13

Experiment 11 was repeated with substrate 3, and a dry film thickness of3-5 μm was also determined using SEM.

EXAMPLES 14-15

As in Examples 11 to 13, substrates 1 to 3 were coated, except that 0.4g/L hexafluorozirconic acid was added instead of 0.4 g/Lhexafluorotitanic acid. A dry film thickness of 8-10 μm was determinedfor substrates 1 and 2 and 3-5 μm for substrate 3, based on measurementswith an eddy current measurement device and SEM.

EXAMPLES 16-19

As in Examples 11 to 13, substrates 1 to 3 were coated except that, inaddition to 0.4 g/L hexafluorotitanic acid, 3 g/L AMEO was also used asan additive. A dry film thickness of 30-35 μm was determined forsubstrate 1, 15-20 μm for substrate 2 and 3-5 μm for substrate 3, basedon measurements with an eddy current measurement device and SEM.

EXAMPLES 20-23

As in Examples 11 to 13, substrates 1 to 3 were coated except that inaddition to 0.4 g/L hexafluorotitanic acid, 3 g/L AMEO was also used asan additive. A dry film thickness of 8-10 μm was determined forsubstrates 1 and 2 and 3-5 μm for substrate 3, based on measurementswith an eddy current measurement device and SEM.

EXAMPLES 24-26

As in Examples 11 to 13, substrates 1 to 3 were coated except that 3 g/LAMEO, 3 g/L gas black pigment and 5 g/L defoaming agent were added as anadditive in addition to 0.4 g/L hexafluorotitanic acid. A dry filmthickness of 30-35 μm was determined for substrate 1, 15-20 μm forsubstrate 2 and 3-5 μm for substrate 3, based on measurements with aneddy current measurement device and SEM.

The micrographs consistently show a homogenous layer has formed, whichindicates a reliable, self-regulating and readily controllable coatingmethod.

The invention claimed is:
 1. Method for coating metallic surfaces ofsubstrates, comprising steps: I. supplying a substrate metallic surface,the metallic surface being cleaned, II. contacting and coating themetallic surface with an aqueous composition in the form of adispersion, suspension or combinations thereof to form an organiccoating on the metallic surface, and III. drying the organic coating,baking the organic coating or combinations thereof, wherein the aqueouscomposition of step II contains 2.5 to 45 wt % of at least onenonionically stabilized binder and 0.1 to 2.0 wt % of a gelling agent,and wherein the aqueous composition has a pH in the range of 0.5 to 7and forms the organic coating based on an ionogenic gel with metalcations dissolved out of the metallic surface during the contacting instep II.
 2. The method according to claim 1, wherein the gelling agentcomprises: a) at least one polysaccharide based on glycogens, amyloses,amylopectins, calloses, agar, algins, alginates, pectins, carrageenan,celluloses, chitins, chitosans, curdlans, dextrans, fructans, collagens,gellan gum, gum arabic, starches, xanthans, gum tragacanth, karayans,tara gum, and glucomannans; b) at least one anionic polyelectrolyte ofnatural origin, based on polyamino acids, collagens, polypeptides, andlignins, c) at least one synthetic anionic polyelectrolyte, based onpolyamino acids, polyacrylic acids, polyacrylic acid copolymers,acrylamide copolymers, lignins, polyvinyl sulfonic acid, polycarboxylicacids, polyphosphoric acids, and polystyrenes, (d) or combinationsthereof.
 3. The method according to claim 1, wherein the gelling agentcomprises at least one polysaccharide, based on pectins, gellan gum orcombinations thereof.
 4. The method according to claim 1, wherein theaqueous composition, the organic coating produced from it, orcombinations thereof contains at least one anionic polysaccharide,selected from those with a degree of esterification, amidation or acombination thereof of the carboxyl function in the range of 1 to 75%,based on the total number of alcohol and carboxy groups.
 5. The methodaccording to claim 1, wherein the aqueous composition, the organiccoating produced from it, or combinations thereof contain at least oneanionic polysaccharide, at least one anionic polyelectrolyte orcombinations thereof selected from those having a molecular weight inthe range of 500 to 1,000,000 g/mol.
 6. The method according to claim 1,wherein the nonionically stabilized binders are modified withadhesion-promoting adhesive groups, selected from the group consistingof chemical groups of multifunctional epoxies, isocyanates, primaryamines, secondary amines, tertiary amines, quaternary amines, amides,imides, imidazoles, formamides, Michael reaction products,carbodiimides, carbenes, cyclic carbenes, cyclocarbonates,multifunctional carboxylic acids, amino acids, nucleic acids,methacrylamides, polyacrylic acids, polyacrylic acid derivatives,polyphenols, polyols having at least one alkyl or aryl radical,caprolactam, phosphoric acids, phosphoric acid esters, epoxy esters,sulfonic acids, sulfonic acid esters, vinyl sulfonic acids, vinylphosphonic acids, catechol, silanes as well as silanols and/or siloxanesproduced from the former, triazines, thiazoles, thiazines, dithiazines,acetals, hemiacetals, quinones, saturated fatty acids, unsaturated fattyacids, alkyds, esters, polyesters, ethers, cyclic ethers, crown ethers,anhydrides as well as acetyl acetones and β-diketo groups, carbonylgroups and hydroxyl groups.
 7. The method according to claim 1, whereinthe aqueous composition, the organic coating produced from it orcombinations thereof contains at least one complexing agent for themetal cations or a polymer modified for complexing the metal cations. 8.The method according to claim 7, wherein the at least one complexingagent is selected from the group consisting of those based on maleicacid, alendronic acid, itaconic acid, citraconic acid, mesaconic acid,or one of the anhydrides and hemiesters of these carboxylic acids. 9.The method according to claim 1, wherein the aqueous composition, theorganic coating produced from it or combinations thereof contains atleast one type of cations selected from those based on cationic saltsselected from the group consisting of melamine salts, nitroso salts,oxonium salts, ammonium salts, salts with quaternary nitrogen cations,salts of ammonium derivatives and salts of Al, B, Ba, Ca, Cr, Co, Cu,Fe, Hf, In, K, Li, Mg, Mn, Mo, Na, Nb, Ni, Pb, Sn, Ta, Ti, V, W, Zn, Zror combinations thereof.
 10. The method according to claim 9, whereinAl, Cu, Fe, Mg, Zn or a combination thereof are selected as the metalcations that have been dissolved out of the metallic surface, that havebeen added to the aqueous composition or combinations thereof.
 11. Themethod according to claim 1, wherein the aqueous composition contains acrosslinking agent selected from the group consisting of: silanes,siloxanes, phenolic resins and amines, in an amount of 0.01 g/L to 50g/L.
 12. The method according to claim 1, wherein the aqueouscomposition contains an amino-functionalized silane in an amount of 0.1g/L to 30 g/L.
 13. The method according to claim 1, wherein the aqueouscomposition contains complex titanium, zirconium fluorides or acombination thereof in an amount of 0.01 g/L to 100 g/L.
 14. The methodaccording to claim 13, wherein the aqueous composition contains complextitanium, zirconium fluorides or a combination thereof in an amount of0.1 g/L to 10 g/L.
 15. The method according to claim 1, wherein theaqueous composition contains at least one additive selected from thegroup, consisting of: defoaming agents, pigments, biocides, dispersionaids, film-forming aids, acidic additives for adjusting the pH, basicadditives for adjusting the pH, thickeners and flow control agents. 16.The method according to claim 1, wherein the organic coating is formedin 0.05 to 20 minutes in an immersion bath and has a dry film thicknessin the range of 5 to 100 μm after drying.
 17. The method according toclaim 1, wherein step III further comprises rinsing the organic coatingbefore at least one of drying the organic coating, baking the organiccoating, and combinations thereof.
 18. The method according to claim 1,wherein step III further comprises drying the organic coating andforming another coating with a similar or additional coating compositionbefore the drying, baking or combinations thereof.